As one of conventional technologies, for example, a normal communication process, which is executed in a communication system that includes at least one base station and a plurality of terminals (including a single terminal) located in a service area covered by the base station is explained below.
For example, the base station has a function of selecting a terminal to which transmission permission is given, out of the plurality of terminals that transmit a data transmission request, that is, has a scheduling function, and each terminal performs data transmission basically according to the scheduling.
Specific operations of the base station and each terminal are explained below (see Nonpatent literature 1). At first, a terminal in which data to be transmitted occurs sends a transmission request for data to the base station. Information here as the transmission request, which a terminal reports to the base station, can include, for example, a data amount retained in a buffer and transmission power that can be output by the terminal, or the like. On the other hand, the base station selects a terminal to which transmission permission is given, based on the information received as a transmission request, based on predicted channel quality upon data transmission from each terminal, and based on an allowable interference level upon reception thereof at the base station. Then, the base station returns an assignment signal as a response to the transmission request. At this time, the base station reports the maximum number of bits to be transmitted which are selectable by the terminal, i.e., a transmission rate (Rate) and a transmission permitted time (Time), to the terminal.
The terminal selected based on the assignment signal performs data transmission based on the information received. At this time, the terminal transmits data within the transmission permitted time.
In 3GPP, retransmission control (ARQ: Automatic Repeat reQuest) in the Physical Layer has been studied (see Nonpatent literature 2), in which a base station that receives data from a terminal returns an ACK signal when reception thereof is successful and an NAK signal when reception thereof is failed. When receiving the NAK signal, the terminal sends again a transmission request before retransmission is performed, receives an assignment signal from the base station, and then, transmits again the same data to the base station.
Nonpatent Literature 1:
3GPP TR25.896 V1.0.0, 7.1.2.2, 7.1.2.3
Nonpatent Literature 2:
3GPP TR25.896 V1.0.0, 7.2
However, in the communication methods described in the above-mentioned literatures, if a terminal has data that should be transmitted and even if the data is retransmission data, it is necessary to send a transmission request to the base station and receive an assignment signal as a response to the transmission request. Therefore, there is such a problem that because transmission of the retransmission data delays, a data group cannot be transmitted to the upper layer although other data has already been received successfully by the base station.
The base station having sent back the NAK signal does not abandon the data resulting in reception failure, but subjects the data upon reception failure to buffering to be used for combination with the data retransmitted. Therefore, if a delay occurs in the retransmission of the data, the time for using a buffer becomes longer, which causes buffer use efficiency to get worse.
The present invention has been achieved to resolve the conventional problems, and it is an object of the present invention to provide a communication method capable of improving buffer use efficiency at a base station by improving a delay in transmission of retransmission data and to provide a terminal and a base station to execute the communication method.